JP2022174209A - Endoscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an endoscope which effectively reduces the passage of excitation light unnecessary for imaging of fluorescent light with a simple structure using one excitation light cutoff filter, realizes shortening of an optical length of imaging optics and suppresses the image quality deterioration of a fluorescent image.

SOLUTION: An endoscope is provided with: imaging optics that comprises a plurality of optical components constituting a light path and that causes light from a subject to enter the light path and form an image, wherein the light includes fluorescent light generated by excitation light that causes the emission of fluorescent light from a fluorescent drug that has been administered to the subject; an image sensor that performs photoelectric conversion of the light from the subject imaged by the imaging optics; and one excitation light cutoff filter, which is disposed in the interior of the imaging optics, and blocks the transmission of at least a portion of the excitation light from the light from the subject.

SELECTED DRAWING: Figure 6

COPYRIGHT: (C)2023,JPO&INPIT

Description

The present disclosure relates to an endoscope that captures fluorescence generated based on excitation light applied to an observation target.

When imaging fluorescence generated in an observation target (e.g., a patient's body) into which an endoscope is inserted, transmission of the excitation light is suppressed in order to minimize the incidence of the excitation light on the imaging target (e.g., the affected area). An excitation light cut filter for blocking is arranged in the imaging optical system of the endoscope. For example, Patent Document 1 discloses an endoscope in which at least two excitation light cut filters are arranged in an imaging optical system. These excitation light cut filters each have the same transmittance characteristics, and have a transmittance in the red to near-infrared light region. The wavelength at which the light transmittance is 0.1% or more and the light transmittance at an incident angle of 0 degree is 50% or more is 680 nm or more.

Japanese Patent No. 5380690

However, in the configuration of Patent Document 1, a plurality of (for example, two) excitation light cut filters are arranged in the optical system, furthermore, the first excitation light cut filter and the second An optical element having power (for example, a biconvex lens) is arranged between and between the excitation light cut filter. For this reason, it is difficult to shorten the total optical length of the imaging optical system, and there has been a problem that manufacturing is not easy.

The present disclosure has been devised in view of the conventional situation described above, with a simple structure using a single excitation light cut filter, effectively reducing the passage of excitation light unnecessary for fluorescence imaging, imaging optics It is an object of the present invention to provide an endoscope that suppresses deterioration in the image quality of fluorescence images while achieving a shortened optical length of the system.

The present disclosure includes a plurality of optical components that configure an optical path, and includes fluorescence based on excitation light for causing a fluorescent agent administered to a subject to emit fluorescence, and light from the subject enters the optical path to be condensed. an imaging optical system for imaging an image; an image sensor for photoelectrically converting light from the subject formed by the imaging optical system; and an excitation light cut filter that blocks transmission of at least part of the excitation light.

In addition, the present disclosure includes a plurality of optical components that constitute an optical path, and allows light from the subject, including fluorescence based on excitation light for causing a fluorescent agent administered to the subject to emit fluorescent light, to enter the optical path. an imaging optical system that forms an image using the imaging optical system; an image sensor that photoelectrically converts the light from the subject that is imaged by the imaging optical system; and an excitation light cut filter, wherein the plurality of optical components includes a first lens and a second lens arranged on the rear end side of the first lens, and adjacent to each other after the first lens The end face and the tip face of the second lens are flat, and the excitation light cut filter is inserted between the rear face of the first lens and the tip face of the second lens adjacent to each other. Provide a speculum.

According to the present invention, with a simple structure using one excitation light cut filter, it is possible to effectively reduce the passage of excitation light unnecessary for imaging fluorescence, and shorten the optical length of the imaging optical system. In addition, deterioration of the image quality of fluorescence images can be suppressed.

1 is a perspective view showing an appearance example of an endoscope system according to Embodiment 1; FIG. A perspective view showing an example of the appearance of the distal end side of the endoscope. Cross-sectional view showing an example of a rigid portion of an endoscope Graph showing an example of band cut filter characteristics and excitation light and fluorescence characteristics Enlarged view of the main part of the characteristics in the wavelength range of 700 to 900 nm in FIG. A diagram showing an example of the arrangement of the first imaging optical system and the incident optical path of light rays. A diagram showing an example of a configuration arrangement of a second imaging optical system and an incident optical path of a light ray. A diagram showing an example of a configuration arrangement of a third imaging optical system and an incident optical path of light rays. A diagram showing an example of a configuration arrangement of a fourth imaging optical system and an incident optical path of light rays. A diagram showing an example of the maximum incident angle (converted to air) corresponding to light rays generated in each of the first to fourth imaging optical systems.

(Circumstances leading to obtaining a form related to the present disclosure)
First, compared to the imaging optical system including a plurality of excitation light cut filters disclosed in Patent Document 1, in order to shorten the total optical length of the imaging optical system, an excitation light cut filter (for example, a band cut filter (BCF: Consider placing only one Band Cut Filter)). The excitation light causes a fluorescent agent (eg, ICG (indocyanine green)) pre-administered to the subject (that is, the observation target into which the insertion portion of the endoscope is inserted. For example, the patient's body) to emit fluorescence. Therefore, the subject is illuminated.

If only one band-cut filter is arranged and the incident angle of the excitation light (for example, 690 nm to 820 nm) incident on the band-cut filter is large, sufficient reflection (in other words, blocking) of the excitation light occurs at the band-cut filter. Otherwise, the excitation light will pass through the band-cut filter. In this case, the excitation light passes through the band cut filter and enters the image sensor side of the imaging optical system. are more likely to occur.

On the other hand, when the incident angle of the excitation light to the band cut filter is less than a predetermined threshold value (for example, 25 degrees), the band cut filter can sufficiently block the incident excitation light. In this case, since the amount of excitation light that forms an image on the image sensor is reduced, it is expected that deterioration in image quality of the image captured by the image sensor can be suppressed.

Therefore, in the following embodiments, a simple structure using one band cut filter is used so that the incident angle of the excitation light to the band cut filter is less than a predetermined threshold value (for example, 25 degrees). The transmission of excitation light (690 nm to 820 nm) unnecessary for fluorescence imaging should be sufficiently blocked.

Hereinafter, embodiments specifically disclosing the configuration, operation, and the like of an endoscope according to the present disclosure will be described in detail with reference to the drawings as appropriate. However, more detailed description than necessary may be omitted. For example, detailed descriptions of well-known matters and redundant descriptions of substantially the same configurations may be omitted. This is to avoid unnecessary verbosity in the following description and to facilitate understanding by those skilled in the art. It should be noted that the accompanying drawings and the following description are provided for a thorough understanding of the present disclosure by those skilled in the art and are not intended to limit the claimed subject matter.

FIG. 1 is a perspective view showing an appearance example of an endoscope system 11 according to Embodiment 1. FIG. In the following description, the directions used for description follow the description of the directions in FIG. Specifically, the upward direction and the downward direction of the housing 27 of the video processor 13 placed on the horizontal plane are referred to as "up" and "down", respectively. Also, the side of the endoscope 15 that captures an image of an observation target is called "front", and the side that is connected to the video processor 13 is called "rear". Also, the right hand side in the direction in which the endoscope 15 is inserted is called "right", and the left hand side in the direction in which the endoscope 15 is inserted is called "left".

The endoscope system 11 includes an endoscope 15 , a video processor 13 and a monitor 17 . The endoscope 15 is, for example, a medical flexible scope. The video processor 13 converts captured images (including, for example, still images and moving images) obtained by imaging an observation target (for example, a human body such as a patient, or an affected part inside the human body) with an endoscope 15. image processing. The video processor 13 sends the image signal obtained by image processing to the monitor 17 as an image signal for display. The monitor 17 displays the captured image of the endoscope 15 image-processed by the video processor 13 according to the display image signal output from the video processor 13 . Image processing includes, but is not limited to, color correction, tone correction, and gain adjustment.

The endoscope 15 is inserted into an observation target (an example of a subject) of a human body such as a patient, and captures an image of the observation target. The endoscope 15 includes a scope 19 to be inserted inside an observation target, and a plug portion 21 to which the rear end portion of the scope 19 is connected. The scope 19 includes a relatively long flexible flexible section 23 and a rigid rigid section 25 provided at the distal end of the flexible section 23 . The structure of scope 19 will be described later.

The video processor 13 has a housing 27, performs image processing on an image captured by the endoscope 15, and outputs an image signal after the image processing as an image signal for display. A socket portion 31 into which the proximal end portion 29 of the plug portion 21 is inserted is arranged on the front surface of the housing 27 . By inserting the plug portion 21 into the socket portion 31 and electrically connecting the endoscope 15 and the video processor 13, electric power and various signals (for example, video signals) are transmitted between the endoscope 15 and the video processor 13. , control signals) can be transmitted and received. These electric power and various signals are led from the plug portion 21 to the flexible portion 23 via a transmission cable 231 (see FIG. 3) inserted inside the scope 19 . An image signal of a captured image output from the image sensor 33 (see FIG. 3) provided inside the rigid portion 25 is transmitted from the plug portion 21 to the video processor 13 via the transmission cable 231 .

In addition, the housing 27 includes a visible light source (not shown) for emitting visible light (white light) and an IR excitation light source (not shown) for emitting excitation light (for example, excitation light in the IR band). is built-in.

The visible light source emits (irradiates) visible light (white light) when operated by a doctor or the like (including a person who assists the doctor or the like; the same shall apply hereinafter). This visible light (white light) is guided to the distal end of the endoscope 15 in the direction of insertion through optical fibers 49, 49 (an example of a light guide) and illuminated toward the observation target.

Similarly, the IR excitation light source emits (irradiates) excitation light in the IR band when operated by a doctor or the like. This excitation light is guided to the distal end of the endoscope 15 in the direction of insertion through optical fibers 39 and 41 (an example of a light guide) and illuminated toward the observation target.

The video processor 13 performs image processing on the image signal transmitted from the endoscope 15 via the transmission cable 231 , converts the processed image signal into an image signal for display, and outputs the image signal to the monitor 17 . do.

The monitor 17 is configured by a display device such as an LCD (Liquid Crystal Display), a CRT (Cathode Ray Tube), or an organic EL (Electroluminescence) display. A monitor 17 displays a captured image of an observation target captured by the endoscope 15 . Specifically, the monitor 17 displays a visible light image obtained by imaging visible light and a fluorescence image generated by imaging fluorescence based on excitation light.

FIG. 2 is a perspective view showing an appearance example of the distal end side of the endoscope 15. As shown in FIG. An imaging window 35 is arranged on the distal end surface of the rigid portion 25 . The imaging window 35 is made of, for example, an optical material such as optical glass or optical plastic, and receives light from an observation target (an example of a subject). The light from the observation object is, for example, light reflected by the observation object when it is irradiated with white light (that is, visible light), or light reflected by the observation object when it is irradiated with excitation light in the IR band. Light (ie, excitation light) and fluorescence caused by the excitation light.

The endoscope 15 irradiates an observation target of a subject with excitation light for fluorescence observation, and emits fluorescence emitted from a fluorescent agent (for example, ICG) previously administered by injection or the like into the subject based on irradiation of the excitation light. An image can be taken and a fluorescence image can be obtained. In such fluorescence observation, for example, ultraviolet light having a wavelength band of 380 nm to 450 nm or IR excitation light having a wavelength band of 690 to 820 nm is used. In Embodiment 1, an example in which IR (Infrared) excitation light is used as excitation light for fluorescence observation will be described below, but the excitation light is not limited to this.

Illumination windows 43 and 45 through which the tips of a pair of optical fibers 39 and 41 for transmitting (guiding) the excitation light from the IR excitation light source are exposed are arranged on the tip surface of the rigid portion 25 . A pair of illumination windows 51 through which the tips of a pair of optical fibers 49 and 50 for transmitting (guiding) visible light from a visible light source are exposed are arranged on the tip surface of the rigid portion 25 . A pair of illumination windows 43 and 45 for IR are arranged on both diametrical end sides of a circular distal end flange 53 provided at the distal end of the rigid portion 25 . Also, a pair of illumination windows 51, 51 for visible light are similarly arranged on both ends of the tip flange 53 in the diametrical direction. The pair of illumination windows 43, 45 for IR and the pair of illumination windows 51, 51 for visible light are, for example, arranged at regular intervals in the circumferential direction. The number of the pair of optical fibers 39, 41 for IR and the number of the pair of optical fibers 49, 49 for visible light may be other than the above.

FIG. 3 is a cross-sectional view showing an example of the rigid portion 25 of the endoscope 15. As shown in FIG. The cross section of FIG. 3 may be represented, for example, by a plane passing through the respective centers of the illumination window 43, the imaging window 35, and the illumination window 45 of FIG. 2, or the illumination window 51 of FIG. , the imaging window 35 and the illumination window 51, respectively.

The endoscope 15 includes a lens unit 235 that supports an imaging optical system by a lens support member 239 so as to be able to accommodate an imaging optical system, an image sensor 33 whose imaging surface 241 is covered with an element cover glass 243, and a lens light at the center of the imaging surface 241. Adhesive resin 37 for fixing lens unit 235 and element cover glass 243 (an example of sensor glass) with aligned axes, and adhesive resin 37 provided on the surface opposite to the imaging surface of image sensor 33 (that is, the rear side). and a transmission cable 231 having four wires 245 connected to each of the four conductor connections 249 .

The lens support member 239 includes a plurality of (three in the illustrated example) plano-convex lenses L1, bi-convex lenses L2, and bi-concave lenses L3 made of an optical material (for example, glass, resin, etc.). Aperture AP1 and , are incorporated in close proximity to each other in the direction of the optical axis. The diaphragm AP1 is provided for adjusting the amount of light incident on the plano-convex lens L1, and only light that has passed through the diaphragm AP1 can enter the plano-convex lens L1. The plano-convex lens L1, the bi-convex lens L2, and the bi-concave lens L3 are fixed to the inner peripheral surface of the lens support member 239 with an adhesive over the entire circumference. In the following description, a plano-concave lens may be provided instead of the biconcave lens L3.

Nickel, for example, is used as the metal material forming the lens support member 239 . Nickel has a relatively high modulus of rigidity and high corrosion resistance, and is suitable as a material for forming the hard portion 25 . In order to prevent the nickel constituting the lens support member 239 from being directly exposed from the hard portion 25 during inspection using the endoscope 15 or during surgery, the surroundings of the lens support member 239 are removed before inspection or surgery. is uniformly coated with the mold resin 217, and the hard portion 25 is preferably coated with a biocompatible coating. Instead of nickel, for example, a copper-nickel alloy may be used. A copper-nickel alloy also has high corrosion resistance and is suitable as a material for forming the hard portion 25 . Moreover, as the metal material forming the lens support member 239, a material that can be manufactured by electroforming (electroplating) is preferably selected.

The image sensor 33 is configured by, for example, a small-sized CCD (Charge Coupled Device) or CMOS (Complementary Metal-Oxide Semiconductor) imaging device having a square shape when viewed from the front and rear directions. In the image sensor 33 , light incident from the outside is condensed by the optical lens group in the lens support member 239 and imaged on the imaging surface 241 . Further, in the image sensor 33, the imaging surface 241 is covered so as to be protected by an element cover glass 243 (for example, sensor glass SG2 described later).

Four conductor connection portions 249 are provided at the rear portion of the image sensor 33 on the back side. The conductor connection part 249 can be formed by, for example, an LGA (Land grid array). The four conductor connections 249 consist of a pair of power connections and a pair of signal connections. The four conductor connections 249 are electrically connected to the four wires 245 of the transmission cable 231 . The transmission cable 231 includes a pair of power lines, which are the electric wires 245 , and a pair of signal lines, which are the electric wires 245 . That is, the pair of power lines of the transmission cable 231 are connected to the pair of power connection portions of the conductor connection portion 249 . A pair of signal lines of the transmission cable 231 are connected to a pair of signal connection portions of the conductor connection portion 249 .

According to this endoscope 15, the lens unit 235 and the image sensor 33 are fixed by the adhesive resin 37 while being held at a predetermined distance. The optical axis of the lens unit 235 and the center of the imaging surface 241 are aligned with the fixed lens unit 235 and the image sensor 33 . In addition, the distance between the lens unit 235 and the image sensor 33 is adjusted so that the incident light from the subject passing through the lens unit 235 is focused on the imaging surface 241 of the image sensor 33 . The lens unit 235 and the image sensor 33 are fixed after being aligned.

A spaced portion is formed between the fixed lens unit 235 and the image sensor 33 . The shape of the spaced portion is determined by relatively aligning the lens unit 235 and the image sensor 33 and fixing them together with the adhesive resin 37 . That is, the spaced portion serves as an adjustment gap for alignment between the lens unit 235 and the image sensor 33 .

FIG. 4 is a graph showing an example of characteristics of a band cut filter and characteristics of excitation light and fluorescence. The endoscope 15 can configure a band cut filter (an example of an IR excitation light cut filter) with a reflective cut filter. In this case, the band-cut filter is a non-absorbing filter, so it is called a dielectric filter (that is, a reflective cut-off filter) and can be distinguished from a metal filter that exhibits absorption.

The band cut filter is an edge filter with sharp boundaries 89 (edges) and boundaries 91 between the transmission band and the stop band. A general requirement for this kind of edge filter is that the transition from the stop band to the transmission band is as sharp as possible and the transmission band is as close to 100% as possible. In the band-cut filter according to Embodiment 1, the wavelength of the excitation light is approximately at the center of the stop band.

FIG. 5 is an enlarged view of the main part of the characteristics in the wavelength range of 700 to 900 nm in FIG. Here, the fluorescence caused by the excitation light is weak and several percent of the excitation light. Indocyanine green (ICG), which is a fluorescent agent for medical use that is harmless to the human body in particular, is administered around an affected area in the body, and an observation site (for example, an affected area where ICG accumulates) is irradiated with excitation light in the IR band to generate fluorescence. It is conceivable that the affected area may be illuminated and imaged. Therefore, the video processor 13 adjusts the gain so as to increase the gain of the fluorescence emission image (fluorescence image). Therefore, even a weak entry of excitation light causes degradation of image quality. Under these circumstances, it is desirable to ensure that the stopband has a sufficient range with respect to the wavelength of the excitation light.

On the other hand, the fluorescence caused by the excitation light has a peak in a gentle wavelength range that is continuous with the wavelength band of the excitation light. Therefore, the boundary 91 between the stopband and transmission band of the band cut filter is important. In other words, there is a demand to capture the fluorescence wavelength Wk as much as possible while separating the boundary 91 from the excitation light wavelength. The band-cut filter has a stopband (transmission forbidden band) including a wavelength corresponding to the peak intensity of the excitation light and a wavelength at which the intensity of the excitation light is 1/Exp2 (that is, e ² ) or less of the peak, and , a wavelength that does not include all of the generated fluorescence wavelength Wk (or a wavelength that includes a part of the generated fluorescence wavelength Wk). e is 2.71828 (abbreviated hereinafter), which is the base of the natural logarithm. That is, the band-cut filter cuts off the wavelength region of the fluorescence wavelength Wk that is particularly weak and close to the excitation light by including it in the stopband. This makes it possible to efficiently capture the effective fluorescence wavelength Wka among the weak fluorescence wavelengths Wk while suppressing the penetration of the excitation light as much as possible.

This reflective band cut filter preferably has a high optical density (OD value). The OD value is desirably 5 or more, for example. By setting the OD value to a high value, the band cut filter can more easily block passage of the excitation light.

Moreover, the endoscope 15 can configure the band cut filter with an absorption cut filter. As the absorption type cut filter, filter glass (absorption type) having less dependency on incident light angle can be used. In the case of this absorption-type band cut filter, the stop band (transmission forbidden band) is equal to or less than the wavelength corresponding to the peak intensity of the excitation light and 1/Exp2 (that is, e ² ) of the peak intensity of the excitation light. and a wavelength that does not include all of the generated fluorescence wavelength Wk (or a wavelength that includes a part of the generated fluorescence wavelength Wk). This provides the same effects as those described above. That is, the absorption-type band-cut filter cuts off the wavelength region of the fluorescence wavelength Wk, which is particularly weak and close to the excitation light, by including it in the stopband. This makes it possible to efficiently capture the effective fluorescence wavelength Wka among the weak fluorescence wavelengths Wk while suppressing the penetration of the excitation light as much as possible.

Next, a configuration and arrangement example of the imaging optical system of the endoscope 15 including the band cut filter will be described with reference to FIGS. 6 to 9. FIG.

(Arrangement of First Imaging Optical System)
FIG. 6 is a diagram showing an example of the arrangement of the first imaging optical system 55 and incident optical paths of light rays. The first imaging optical system 55 includes an objective cover glass CG1, an aperture AP1, a plano-convex lens L1, and a flat plate along the optical axis from the distal end side of the endoscope 15 (in other words, the objective side or the excitation light incident side). A glass FG1, a biconvex lens L2, a biconcave lens L3, and a sensor glass SG2 are arranged in this order.

In the first imaging optical system 55, a deposited film of the band cut filter 111 is formed on the front end side surface of the flat glass FG1 (that is, the surface on the planoconvex lens L1 side). In the first imaging optical system 55, the vapor-deposited film of the band cut filter 111 is formed on the surface of the flat glass FG1 on the imaging side (that is, the surface on the biconvex lens L2 side) or on both sides of the flat glass FG1. may be The thickness of the flat glass FG1 is, for example, 0.30 mm.

Also, an adhesive having a refractive index larger than that of air, for example, is filled between the biconvex lens L2 and the biconcave lens L3 to form an adhesive layer between the biconvex lens L2 and the biconcave lens L3. Since the biconvex lens L2 is brought into close contact with the biconcave lens L3 by this adhesive layer, no air layer is interposed between the biconvex lens L2 and the biconcave lens L3. Moreover, the image sensor 33 is arranged on the rear surface (rear surface) of the sensor glass SG2.

Aperture AP1 acts as an aperture stop that restricts the passage of incident light by limiting the angle of incidence and corresponds to the f-number. Aperture AP1 passes only the portion of the light (see above) from the observation target that is desired to form an image. The chief ray passes through the center of the aperture even when the aperture stop is fully closed. In the endoscope 15, the light passing through the aperture AP1 is collected by the first imaging optical system 55 and formed into an image by the image sensor 33. FIG.

In the first imaging optical system 55, the incident light b1 including the excitation light passes through the aperture AP1 and enters the plano-convex lens L1. It enters the formed band cut filter 111 . In this case, the angle of incidence on the band cut filter 111 (that is, the angle from the direction perpendicular to the band cut filter 111) is reduced by the plano-convex lens L1 having the power to refract light rays. In other words, the incident light b1 enters the band cut filter 111 with an inclination close to vertical (in other words, an incident angle close to 0 degrees). The band cut filter 111 can efficiently reflect the excitation light contained in the incident light b1 and sufficiently block its transmission.

For example, when the image height FA at which the incident angle is considered to be the largest is 1.0 (that is, the position farthest from the center of the band cut filter 111 in the incident light to the band cut filter 111), We simulate the case where a ray is incident on the bandcut filter 111 . In this case, according to the arrangement of the first imaging optical system 55, the incident angle (that is, the maximum ray angle) to the band cut filter 111 is 24.9 degrees in terms of air, and a predetermined threshold value (for example, 25 degrees) ) (see FIG. 10). The predetermined threshold value indicates an incident angle of light at which the light incident on the band cut filter can be sufficiently reflected (that is, it is difficult for the light to pass through).

The incident light b2 transmitted through the band cut filter 111 passes through the biconvex lens L2 and the biconcave lens L3, converges, and forms an image on the image sensor 33 arranged on the back surface (rear surface) of the sensor glass SG2.

Here, Table 1 shows lens data related to various lenses and the band cut filter 111 (BCF) that constitute the first imaging optical system 55 . Here, BF represents the back focus (the distance from the rear end of the lens to the image sensor), and so on.

As described above, in the first imaging optical system 55, the vapor-deposited film of the band cut filter 111 is formed on one surface (for example, the surface on the object side) of the flat glass FG1, and the band cut filter 111 faces the plano-convex lens L1. In addition, the flat plate glass FG1 is arranged between the planoconvex lens L1 and the biconvex lens L2, so that the configuration and arrangement can be easily performed. Therefore, it is possible to easily manufacture the first imaging optical system 55 and the endoscope 15 in which only one band cut filter 111 is arranged.

The surface on which the vapor-deposited film of the band cut filter 111 is formed may be the rear surface of the flat glass FG1 (surface on the image sensor side). In addition, vapor deposition films of the band cut filter 111 may be formed on both the front surface (object side surface) and the back surface (imaging side surface) of the flat glass FG1. In any of these cases, the same effect as when the band cut filter 111 is formed on the surface of the flat glass FG1 (that is, the incident angle of the upper ray with the image height FA of 1.0 to the band cut filter 111 is less than 25 degrees, and the effect of appropriately blocking the excitation light is obtained.

(Arrangement of Second Imaging Optical System)
FIG. 7 is a diagram showing an example of the arrangement of the second imaging optical system 56 and incident optical paths of light rays. In the description of the second imaging optical system 56, the same components as those of the first imaging optical system 55 are denoted by the same reference numerals to simplify or omit the description of their configurations and actions, and only the different contents will be described. .

In the second imaging optical system 56, the flat glass FG1 on which the vapor-deposited film of the band cut filter 111 is formed is omitted from the configuration of the first imaging optical system 55. FIG. That is, the deposited film of the band cut filter 112 is formed on the lens surface (specifically, the curved surface of the convex lens) of the plano-convex lens L1 on the output side. The second imaging optical system 56 includes an objective cover glass CG1, an aperture AP1, a planoconvex lens L1, a band A cut filter 112, a biconvex lens L2, a biconcave lens L3, and a sensor glass SG2 are arranged in this order.

In the second imaging optical system 56, the incident light b1 including the excitation light passes through the aperture AP1 and enters the plano-convex lens L1, where it converges in the optical axis direction. Incident light in the plano-convex lens L1 enters a band cut filter 112 formed on the curved surface of the lens on the exit side.

In this case, the incident light b1 is emitted with an inclination nearly perpendicular to the curved surface of the plano-convex lens L1 on the exit side. That is, the angle of incidence (the angle from the normal direction of the band cut filter 112) to the band cut filter 112 formed on the curved surface of the lens on the output side is small. The light enters the band cut filter 112 at an inclination close to vertical (in other words, an incident angle close to 0 degrees). The band cut filter 112 can reflect the excitation light contained in the incident light b1 and sufficiently block its transmission.

For example, a case is simulated in which upper and lower rays incident on the position where the image height FA is 0.0 (that is, the central position of the band cut filter 112), where the incident angle is considered to be the largest, enter the band cut filter 112. FIG. In this case, according to the arrangement configuration of the second imaging optical system 56, the incident angle (that is, the maximum ray angle) to the band cut filter 112 is 13.7 degrees in terms of air, which is the predetermined threshold value (25 degrees). was less than (see Figure 10).

The incident light b2 transmitted through the band cut filter 112 passes through the biconvex lens L2 and the biconcave lens L3, converges, and forms an image on the image sensor 33 arranged on the back surface (rear surface) of the sensor glass SG2.

Here, Table 2 shows lens data relating to various lenses and the band cut filter 112 (BCF) that constitute the second imaging optical system 56 .

As described above, in the second imaging optical system 56, the deposited film of the band cut filter 112 is formed on the curved surface of the plano-convex lens L1. Therefore, the configuration of the flat glass FG1 on which the deposited film of the band cut filter 111 of the first imaging optical system 55 is formed can be omitted. As a result, compared with the first imaging optical system 55, the total optical length of the second imaging optical system 56 can be further shortened, the second imaging optical system 56 can be designed in a compact shape, and the second imaging optical system 56 can be further shortened. Manufacture of the optical system 56 and the endoscope 15 can be made easier.

(Arrangement of Third Imaging Optical System)
FIG. 8 is a diagram showing an example of the arrangement of the third imaging optical system 57 and incident optical paths of light rays. In the description of the third imaging optical system 57, the same components as those of the first imaging optical system 55 are denoted by the same reference numerals to simplify or omit the description of their configurations and actions, and only the different contents will be described. .

In the third imaging optical system 57, as in the second imaging optical system 56, the flat glass FG1 on which the vapor-deposited film of the band cut filter 111 is formed is omitted. Specifically, the biconvex lens L2 is composed of a plano-convex lens L2f on the entrance side and a plano-convex lens L2b on the exit side, each of which has a flat cross section perpendicular to the optical axis. A vapor-deposited film of the band cut filter 113 is formed on either one of the rear surface (rear surface) of the plano-convex lens L2f and the front surface of the plano-convex lens L2b.

After the deposited film is formed, the back surface of the plano-convex lens L2f and the front surface of the plano-convex lens L2b are bonded together with an adhesive or the like with the deposited film of the band cut filter 113 interposed therebetween. This glue has a higher refractive index than air. As a result, a biconvex lens L2 in which the band cut filter 113 is arranged is formed. The inside of the biconvex lens L2 is the area where the angle of rays is the smallest in the third imaging optical system 57 . Therefore, the light can be incident on the band cut filter 113 from a nearly perpendicular direction (in other words, an incident angle close to 0 degrees). The third imaging optical system 57 includes an objective cover glass CG1, an aperture AP1, a plano-convex lens L1, and both sides along the optical axis from the distal end side of the endoscope 15 (in other words, the objective side or the excitation light incident side). A convex lens L2 (specifically, a plano-convex lens L2f, a band cut filter 113, and a plano-convex lens L2b), a biconcave lens L3, and a sensor glass SG2 are arranged in this order.

In the third imaging optical system 57, the incident light b1 including the excitation light passes through the aperture AP1 and enters the plano-convex lens L1. Incident. Inside the plano-convex lens L2f, the inclination of the light ray angle is small, and the direction is nearly perpendicular to the band cut filter 113 interposed between the plano-convex lens L2f and the plano-convex lens L2b (in other words, the incident angle is close to 0 degrees). Light rays enter from The band cut filter 113 can efficiently reflect the excitation light contained in the incident light b1 and sufficiently block its transmission.

For example, when the image height FA at which the incident angle is considered to be the largest is 1.0 (that is, the position farthest from the center of the band cut filter 113 in the light incident on the band cut filter 113), We simulate the case where a ray is incident on the bandcut filter 113 . In this case, the incident angle (that is, the maximum ray angle) to the band cut filter 113 was 17.1 degrees in terms of air, which was less than the predetermined threshold value (25 degrees) (see FIG. 10).

Here, when the band cut filter 113 is arranged inside the biconvex lens L2, the incident light to the band cut filter 113 is not from the air but from the lens medium. Therefore, in the lens medium, the incident angle θ2 to the band cut filter can be calculated according to Equation (1) according to Snell's law.

In Equation (1), nd1 is the refractive index of air and has a value of 1. nd2 is the refractive index of the lens medium and has a value of 1.77. θ11 is the incident angle to air, which is 17.1 degrees. θ2 is the incident angle to the lens medium.

As a result of calculation, θ2 was 9.6 degrees in terms of lens medium. Therefore, the incident angle to the band cut filter 113 becomes even closer to the vertical direction (that is, the incident angle becomes closer to 0 degree) according to the arrangement of the third imaging optical system 57 .

The incident light b2 transmitted through the band cut filter 112 passes through the plano-convex lens L2b of the biconvex lens L2 and the biconcave lens L3, converges, and forms an image on the image sensor 33 arranged on the back surface (rear surface) of the sensor glass SG2. .

Here, lens data relating to various lenses and the band cut filter 111 (BCF) constituting the third imaging optical system 57 are shown.

Thus, in the third imaging optical system 57, as in the second imaging optical system 56, the total optical length of the third imaging optical system 57 can be further shortened compared to the first imaging optical system 55. The third imaging optical system 57 can be designed in a compact shape, and the manufacturing of the third imaging optical system 57 and the endoscope 15 can be facilitated. Moreover, since the excitation light is reflected inside the lens, the angle of incidence inside the lens is smaller than the angle of incidence from the air. As a result, light rays enter the band cut filter from a nearly perpendicular direction. Also, in the region of the biconvex lens L2, the light rays are closest to the optical axis direction in the third imaging optical system 57, so the light rays can enter the band cut filter 113 from a direction that is even closer to the perpendicular. Therefore, the excitation light can be efficiently reflected by the band cut filter 113 .

(Arrangement of Fourth Imaging Optical System)
FIG. 9 is a diagram showing an example of the configuration and arrangement of the fourth imaging optical system 58 and incident optical paths of light rays. In the fourth imaging optical system 58, the same components as those in the first imaging optical system 55 are denoted by the same reference numerals to simplify or omit the description of their configurations and actions, and the different contents will be described.

In the fourth imaging optical system 58, like the second imaging optical system 56 and the third imaging optical system 57, the flat glass FG1 on which the vapor-deposited film of the band cut filter 111 is formed is omitted. Specifically, the two lenses L10 in the front stage (object side) are configured as lenses for reducing chromatic aberration of incident light, and are combined with a concave-convex lens L11 and a concave-convex lens L12. The two lenses for reducing chromatic aberration are not limited to the example shown in FIG. 9, and may be a combination of a biconcave lens and a biconvex lens.

The rear-stage lens L20 is composed of a plano-convex lens L21 and a plano-concave lens L22 having a flat cross section perpendicular to the optical axis. A vapor-deposited film of the band cut filter 114 is formed on either one of the rear surface (rear surface) of the plano-convex lens L21 and the front surface of the plano-concave lens L22.

After the deposited film is formed, the back surface of the plano-convex lens L21 and the front surface of the plano-concave lens L22 are bonded together with an adhesive or the like with the deposited film of the band cut filter 114 interposed therebetween. This glue has a higher refractive index than air. As a result, the rear lens L20 is molded into a concave-convex lens in which the band cut filter 114 is arranged. The inside of this concave-convex lens is a region where the inclination of the light angle is the smallest. Therefore, light rays can be incident on the band cut filter 114 from a direction close to perpendicular (in other words, an incident angle close to 0 degrees). The fourth imaging optical system 58 includes an objective cover glass CG1, an aperture AP1, a lens L10 (specifically, , a concave-convex lens L11, a concave-convex lens L12), a lens L20 (specifically, a plano-convex lens L21, a band cut filter 114, a plano-concave lens L22), and a sensor glass SG2 are arranged in this order.

In the fourth imaging optical system 58, the incident light b1 including the excitation light passes through the aperture AP1 and enters the front lens L10, is converged in the optical axis direction by the front lens L10, and enters the rear lens L20. . At this time, in the front lens L10, the chromatic aberration of the incident light is reduced by the concave-convex lens L11 and the concave-convex lens L12. As a combination of lenses for reducing chromatic aberration, for example, there is an achromatic lens that cancels (cancels) color shift (chromatic aberration) by combining a convex lens made of crown-based glass and a concave lens made of flint-based glass.

A light ray emitted from the front lens L10 enters the rear lens L20. Inside the rear-stage lens L20, the inclination of the ray angle is small, and the direction is nearly perpendicular to the band-cut filter 114 interposed between the plano-convex lens L21 and the plano-concave lens L22 (in other words, the incident angle is close to 0 degrees). Light rays enter from The band cut filter 114 can efficiently reflect the excitation light contained in the incident light b1 and sufficiently block its transmission.

For example, the position where the image height FA at which the incident angle is considered to be the largest is 0.6 (that is, the distance from the center of the band cut filter 114 to the upper end of the incident light to the band cut filter 114 is 60%. position ) is incident on the band-cut filter 114 . In this case, the incident angle (that is, the maximum ray angle) to the band cut filter 114 was 9.5 degrees in terms of air, which was smaller than the predetermined threshold value (25 degrees) (see FIG. 10).

The incident light b2 transmitted through the band cut filter 114 converges through the plano-concave lens L22 and forms an image on the image sensor 33 arranged on the back surface of the sensor glass SG2.

Here, lens data relating to various lenses and the band cut filter 111 (BCF) constituting the third imaging optical system 57 are shown.

Thus, in the fourth imaging optical system 58, as in the second imaging optical system 56 and the third imaging optical system 57, compared to the first imaging optical system 55, the fourth imaging optical system 58 has a total The optical length can be further shortened, the fourth imaging optical system 58 can be designed in a compact shape, and the fourth imaging optical system 58 and the endoscope 15 can be manufactured more easily. Moreover, since the excitation light is reflected inside the lens, the incident angle inside the lens is smaller than the incident angle when converted to air. Also, in the area of the lens L20 in the rear stage, the light rays are in the direction closest to the optical axis in the fourth imaging optical system 58, so the light rays can enter the band cut filter from a direction that is even closer to the perpendicular. Therefore, the excitation light can be efficiently reflected by the band cut filter, and the transmission of the excitation light can be blocked.

FIG. 10 is a diagram showing an example of maximum incident angles (air conversion) corresponding to generated light rays in each of the first to fourth imaging optical systems. As described above, the maximum ray angle is less than the predetermined threshold value (25°) in any one of the first imaging optical system 55 to the fourth imaging optical system 58 .

As described above, in the first imaging optical system 55 to the fourth imaging optical system 58, compared with the conventional case where two or more band cut filters are arranged, only one band cut filter is arranged. The total optical length of the imaging optical system can be shortened.

In particular, only in the second imaging optical system 56 to the fourth imaging optical system 58, by forming a band cut filter as a vapor deposition film inside or outside the lens, like the first imaging optical system 55 The thickness of the flat glass (0.3 mm) can be saved compared to the case where the vapor deposition film is formed on the flat glass FG1, and the total optical length of the imaging optical system can be further shortened accordingly. In addition, in the case of a single band-cut filter, if the excitation light is incident on the surface at an angle close to the perpendicular direction, the reflectance of the excitation light increases. Inability to reflect light. Therefore, by forming a band-cut filter by vapor deposition in a region where the incident angle becomes small, the band-cut filter can efficiently reflect the excitation light.

As described above, the endoscope 15 according to Embodiment 1 allows the light from the subject, including the visible light from the subject or the fluorescence based on the excitation light for causing the fluorescent agent administered to the subject to fluoresce, to enter the optical path. It has an image pickup optical system (for example, the first image pickup optical system 55) that forms an image. The endoscope 15 has an image sensor 33 that photoelectrically converts light from a subject imaged by the first imaging optical system 55 . Only one endoscope 15 is arranged inside the first imaging optical system 55, and a band cut filter 111 (an example of an excitation light cut filter) that cuts off transmission of at least part of the excitation light among the light from the subject. ).

In the first imaging optical system 55, the objective cover glass CG1, the diaphragm AP1, the plano-convex lens L1, the flat glass FG1, the bi-convex lens L2, the bi-concave lens L3, and the sensor glass SG2 (the optical path is set along the optical axis from the tip side). An example of a plurality of constituent optical components) are arranged in order. As a result, the endoscope 15 has a simple structure using a single band-cut filter, and can effectively reduce the passage of excitation light that is unnecessary for imaging fluorescence. can suppress the deterioration of the image quality of the captured image due to the excitation light.

Further, in the first imaging optical system 55, the band cut filter 111 (an example of an excitation light cut filter) is provided on the object side of the flat glass FG1 adjacent to the plano-convex lens L1 (an example of the optical component closest to the object) and on the imaging side. formed on either or both sides. Note that the band cut filter 111 may be formed between the plurality of optical components or in the flat glass FG1 adjacent to the plurality of optical components closest to the object side. Thereby, the imaging optical system of the endoscope 15 including the band cut filter 111 can be easily manufactured.

Also, in the third and fourth imaging optical systems 57 and 58, the band cut filters 113 and 114 (an example of the excitation light cut filter) are one of the optical components interpolated (for example, both optical components). It is formed by planar vapor deposition on the convex lens L2 and lens L20). As a result, light can be incident from a direction close to the optical axis (in other words, an incident angle close to 0 degrees), and the amount of excitation light received by the image sensor 33 is reduced. Also, the total optical length of the imaging optical system can be shortened.

Further, in the third and fourth imaging optical systems 57 and 58, the surfaces of the band cut filters 113 and 114 are adjacent to any one of the biconvex lenses L2 and L20 (for example, the plano-convex lens L2f or the plano-convex lens). L2b, or a convex-plano lens L21 or a plano-concave lens L22), and the adhesion is filled with an adhesive having a higher refractive index than air. As a result, light can be incident from a direction close to the optical axis (in other words, an incident angle close to 0 degrees), and the amount of excitation light received by the image sensor 33 is reduced.

Also, in the first imaging optical system 55, the surface of the band cut filter 111 has a gap (that is, an air layer) between any adjacent optical component (for example, the plano-convex lens L1). As a result, the light beam can be incident from a direction close to the optical axis without being spread by the gap, and the amount of excitation light received by the image sensor 33 is reduced.

Also, in the second imaging optical system 56, the band cut filter 112 is formed by vapor deposition on the curved surface of any adjacent optical component (for example, the plano-convex lens L1). As a result, even if the light ray is diffused in a direction other than a direction close to the optical axis, it can be incident at an incident angle close to the normal direction of the band cut filter 112, and the amount of excitation light received by the image sensor 33 is reduced. Moreover, the total optical length of the imaging optical system can be shortened.

In addition, in the fourth imaging optical system 58, optical components other than any one of the optical components (for example, the front lens L10) include two or more lenses capable of reducing chromatic aberration (for example, the concave-convex lens L11 and the concave-convex lens L11). It is composed of a combination of lenses L12). As a result, the chromatic aberration can be reduced, the transmission of the excitation light can be blocked regardless of the color difference, and the amount of the excitation light received by the image sensor 33 can be reduced.

Also, the band cut filter is formed by vapor deposition on any one of the plurality of optical components forming the imaging optical system. As the angle dependence of the band cut filter, the light beam angle at which the intensity of the excitation light is ¹ /e2 or less of the peak is θL, the refractive index of the optical component in which the band cut filter is formed is nL, and the light to the band cut filter is When the incident angle is θF, θF=sin ⁻¹ (nL*sinθL) is the excitation light formed on or inserted into another part (that is, another optical component) It satisfies the relation smaller than the angle of incidence on the cut filter (* indicates a multiplication operator). As a result, the excitation light whose intensity is 1/e ² or more of the peak can be reflected and the transmission thereof can be blocked, and the amount of the excitation light received by the image sensor 33 can be reduced.

Further, the band cut filters 111, 112, 113, and 114 are composed of reflective cut filters, and the wavelength corresponding to the peak intensity of the excitation light and the intensity of the excitation light are 1/e ² or less of the peak as the transmission prohibited band. and part of the wavelength band of the fluorescence generated based on the excitation light, or not including the entire wavelength band of the fluorescence. As a result, it is possible to reliably block the transmission of the excitation light and allow the fluorescence to be transmitted. In other words, it is possible to efficiently take in the effective fluorescence wavelength among the weak fluorescence wavelengths while suppressing the entrance of the excitation light as much as possible.

The band-cut filters 111, 112, 113, and 114 are composed of absorption ^- type cut filters. and part of the wavelength band of the fluorescence generated based on the excitation light, or not including the entire wavelength band of the fluorescence. As a result, it is possible to reliably block the transmission of the excitation light and allow the fluorescence to be transmitted. In other words, it is possible to efficiently take in the effective fluorescence wavelength among the weak fluorescence wavelengths while suppressing the entrance of the excitation light as much as possible.

Various embodiments have been described above with reference to the drawings, but it goes without saying that the present disclosure is not limited to such examples. It is obvious that a person skilled in the art can conceive of various modifications, modifications, substitutions, additions, deletions, and equivalents within the scope of the claims. Naturally, it is understood that it belongs to the technical scope of the present disclosure. In addition, the constituent elements of the various embodiments described above may be combined arbitrarily without departing from the gist of the invention.

For example, in the above-described embodiment, the band cut filter is a reflective band cut filter that blocks the transmission of the excitation light by reflecting the excitation light. The present disclosure is similarly applicable even when an absorptive band cut filter that blocks light transmission is used.

This application is based on a Japanese patent application (Japanese Patent Application No. 2018-185223) filed on September 28, 2018, the content of which is incorporated herein by reference.

The present disclosure is a simple structure using a single excitation light cut filter, effectively reducing the passage of excitation light unnecessary for imaging fluorescence, and shortening the optical length of the imaging optical system. It is useful as an endoscope that suppresses degradation of image quality of fluorescence images.

15 Endoscope 25 Hard part 33 Image sensor 53 Tip flange 55 First imaging optical system 56 Second imaging optical system 57 Third imaging optical system 58 Fourth imaging optical system 111, 112, 113, 114 Band cut Filter AP1 Diaphragm CG1 Objective cover glass FG1 Flat glass L1 Plano-convex lens L2 Bi-convex lens L2f Plano-convex lens L2b Plano-convex lens L20 Lens L21 Plano-convex lens L22 Plano-concave lens SG2 Sensor glass

However, in the configuration of Patent Document 1, a plurality of (for example, two) excitation light cut filters are arranged in the optical system, furthermore, the first excitation light cut filter and the second An optical element having power (for example, a biconvex lens) is arranged between and between the excitation light cut filter .

The present disclosure has been devised in view of the above-described conventional situation, and aims to provide an endoscope capable of achieving both simplification of the structure of the imaging optical system and suppression of deterioration in image quality of fluorescence images .

Advantageous Effects of Invention According to the present invention, it is possible to provide an endoscope capable of achieving both simplification of the structure of an imaging optical system and suppression of deterioration in image quality of a fluorescence image .

Claims (15)

Imaging optics that has a plurality of optical components that form an optical path and forms an image by causing light from the subject, including fluorescence based on excitation light for causing a fluorescent agent administered to the subject to emit fluorescence, to enter the optical path. system and
an image sensor that photoelectrically converts light from the subject imaged by the imaging optical system;
An excitation light cut filter that is arranged only one in the imaging optical system and blocks transmission of at least part of the excitation light among the light from the subject,
Endoscope. The excitation light cut filter is located between the plurality of optical components, or on one or both of the object side and the imaging side of the flat glass adjacent to the optical component closest to the object side or the most imaging side of the plurality of optical components. formed to
The endoscope according to claim 1. The excitation light cut filter is formed by planar deposition on any one of the plurality of optical components to be inserted,
The endoscope according to claim 1. The surface of the excitation light cut filter is bonded to any adjacent optical component, and the bonding is filled with an adhesive having a higher refractive index than air.
The endoscope according to claim 1. The surface of the excitation light cut filter has a gap between any adjacent optical component,
The endoscope according to claim 1. The excitation light cut filter is formed by vapor deposition on a curved surface of any adjacent optical component,
The endoscope according to claim 1. Other optical components other than any of the optical components are composed of a combination of two or more lenses capable of reducing chromatic aberration.
The endoscope according to claim 3. The excitation light cut filter is formed by vapor deposition on any one of the plurality of optical components,
As the angular dependence of the excitation light cut filter, the light angle at which the intensity of the excitation light is ¹ /e2 or less of the peak is θL, and the refractive index of any of the optical components in which the excitation light cut filter is formed nL, and the incident angle of light to the excitation light cut filter is θF,
satisfies the relation that θF=sin ⁻¹ (nL*sin θL) is smaller than the incident angle to the excitation light cut filter inserted in another part (* indicates a multiplication operator),
The endoscope according to any one of claims 1-7. The excitation light cut filter is composed of a reflective cut filter, and has a wavelength corresponding to the peak intensity of the excitation light and a wavelength at which the intensity of the excitation light is ¹ /e2 or less of the peak as a transmission prohibited band. and a wavelength that includes part of the wavelength band of fluorescence generated based on the excitation light or does not include all of the wavelength band of fluorescence,
The endoscope according to any one of claims 1-8. The excitation light cut filter is composed of an absorption cut filter, and has a wavelength corresponding to the peak intensity of the excitation light and a wavelength at which the intensity of the excitation light is ¹ /e2 or less of the peak as a transmission prohibited band. and a wavelength that includes part of the wavelength band of fluorescence generated based on the excitation light or does not include all of the wavelength band of fluorescence,
The endoscope according to any one of claims 1-8. Imaging optics that has a plurality of optical components that form an optical path and forms an image by causing light from the subject, including fluorescence based on excitation light for causing a fluorescent agent administered to the subject to emit fluorescence, to enter the optical path. system and
an image sensor that photoelectrically converts light from the subject imaged by the imaging optical system;
an excitation light cut filter that blocks transmission of at least part of the excitation light among the light from the subject,
The plurality of optical components includes a first lens and a second lens arranged on the rear end side of the first lens,
a rear end face of the first lens and a front end face of the second lens adjacent to each other are flat;
The excitation light cut filter is inserted between the rear end surface of the first lens and the front end surface of the second lens adjacent to each other,
Endoscope. The excitation light cut filter is formed by vapor deposition on at least one of the rear end surface of the first lens and the front end surface of the second lens,
The endoscope according to claim 11. The first lens is a plano-convex lens, and the second lens is a plano-convex lens,
The endoscope according to claim 11. wherein the first lens is a plano-convex lens and the second lens is a plano-concave lens;
The endoscope according to claim 11. A region between the rear end surface of the first lens and the front end surface of the second lens is a region with the smallest ray angle in the imaging optical system,
The endoscope according to claim 11.

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